Field of the Invention
The invention relates to an electrical interruption switch, in particular for interrupting high currents at high voltages.
Description of Related Art
Such switches are used for instance in power plant and motor vehicle technology for the defined, fast disconnection of high-current electrical circuits in an emergency. There is a need for a switch of this kind in which its tripping and interruption function must be reliably ensured even without maintenance, even for as long as up to 20 years. Moreover, no additional potential danger from hot gas, particles, ejected pieces, plasma, or high voltages induced in the circuit that has been shut off must originate in such a switch.
One possible area of application in motor vehicle technology is the defined, irreversible disconnection of the on-board wiring from the car battery or drive battery shortly after an accident, for the sake of avoiding ignition sources from sparks and plasma that occur for instance if cable insulations are sheared off by sheet-metal parts of the vehicle body penetrating during the accident, or if loose cable ends press against one another or against sheet-metal parts and are sheared off. If gasoline also escapes in an accident, such ignition sources can ignite ignitable mixtures of gasoline and air that accumulate under the hood of the engine, for instance. Additional areas of application are the electrical disconnection of a component assembly from the on-board electrical system in the event of a short circuit in that component assembly, such as a separate electric heater or electric brake, and an emergency shutoff of a lithium battery of the kind used today in electrical and hybrid vehicles as well as in aircraft. These batteries, with a small structural volume, have a high terminal voltage of up to 1200 V with extremely low internal resistance. Both factors can potentially cause a short-circuit current of up 5000 A, without a major drop in the source voltage. For an emergency shutoff of individual solar cell modules or entire large-scale solar cell installations if necessary, the interruption switch presented here is highly suitable because it can be embodied to be triggerable or remote-controllable. Furthermore, it can be embodied such that, in addition or instead, it trips passively, that is, like a conventional safety fuse.
Pyrotechnical fuses that are triggered actively for tripping are known in the prior art. For instance, DE 2 103 565 describes a current interrupter which includes a metal casing that is connected, at two terminal regions spaced apart from one another, in each case to an end of a conductor that is to be made safe. The current path extends via the casing. A pyrotechnical element that is formed by an explosive charge is provided in the casing. The explosive charge is activatable by an electrical igniter, which includes an ignition element that is vaporized by a feed current. The casing is filled with an insulating fluid. The axially elongated casing has an encompassing groove along which the casing tears if the explosive charge is ignited. The casing is then broken apart into two parts that are electrically separate from one another, so that the applicable current circuit is cut. The plasma generated when a current circuit with very high current intensity is cut is extinguished in this current interrupter by the atomized insulating fluid. The tripping can be effected in a motor vehicle by means of the signal of a shock sensor, for instance.
Because the entire sheath would have to be heated up to the tripping temperature and then a detonation-type reaction would not be achieved for certain, self-tripping for disconnecting the current circuit if the conductor to be secured is overloaded is not provided in this known device. This is because it is difficult to ignite an explosive, or in other words to cause it to react by detonating, simply by heating the sheath. However, in the casing form described in DE 2 103 565, for example, this kind of ignition or detonation would be necessary.
It should be mentioned that in pyrotechnics, the term “detonative reaction” is used worldwide if flame-front speeds that by definition are higher than 2000 m/s are reached.
A further disadvantage of this known device is the problem of obtaining permits for devices that have component assemblies filled with explosives or even detonators. For that reason, such devices have so far not come to be used commercially. They are employed only very rarely, in research institutes for special experiments. This is also due to their very poor handling safety and their extremely great potential danger, which can be kept within bounds only with great difficulty.
In many cases, there is also a need for a self-tripping function of such a switch or fuse device, for instance in order, without additional expense for overload sensors, to protect a cable against overload or in the event of a failure of the tripping sensor system or tripping circuit. Such a switch should therefore not only be capable of being tripped controllably but should also have the function of a conventional high-current safety fuse, in the form of a safety fuse that anyone can handle safely, as is the case with conventional safety fuses.
High-current safety fuses of this kind have the disadvantage of a shutoff time which fluctuates within a wide bandwidth after the rated amperage of the fuse has been reached. A cable thus protected can therefore be tasked with only a very slight proportion, such as 30%, of its current-carrying capacity, as otherwise a cable fire, for example, can occur in the event of an overload.
From DE 197 49 133 A1, an emergency shutoff switch for electrical circuits is known that makes both self-tripping and triggerable tripping possible. To that end, an electrical conductor is used which has a pyrotechnical core. This core can for instance comprise a charge of propellant powder. The pyrotechnical core can be ignited on the one hand by heating of the electrical conductor if a permissible current intensity (rated current intensity) is exceeded. On the other, provision is made such that the pyrotechnical core is ignited by a triggerable ignition device, for instance in the form of a glow wire. DE 197 49 133 A1, however, merely describes the principle of such a device but gives no clues whatever about possible embodiments that could advantageously be feasibly constructed. This is because producing a conductor with this kind of pyrotechnical core entails considerable effort and expense. Furthermore, even in this kind of emergency shutoff switch, secure, fast disconnection of the conductor can be ensured only if a detonative explosive substance is employed. In deflagrating substances, that is, substances that cannot be made to react detonatively, such as thermite or nitrocellulose powder, all that happens is that the conductor bursts, and the remaining gas escapes without the conductor being completely disconnected. Complete disconnection is then at best achieved by the complete melting of the conductor as a consequence of the current flowing via the fuse. However, at higher voltages, in particular at switching voltages of merely more than 100 V, this would necessarily lead to ion generation and thus plasma formation in the fuse and hence would highly likely prevent the interruption of the circuit.
From DE 100 28 168 A1 of the present applicant, an electrical switch, in particular for switching high currents, is known that can be embodied both actively, that is, by means of a triggerable ignition device, and passively, that is, via the amperage of the current to be switched off. The switch has a casing which includes a contact unit; the contact unit has two connection contacts connected in stationary fashion to the casing or embodied in one piece with it, for supplying and carrying away an electrical current to be switched, and the two connection contacts, in the starting state of the switch, are electrically conductively connected inside the casing. In the casing, an activatable material is provided, which after the activation generates a gas pressure for imposition on the contact unit, wherein the electrically conductive connection is disconnected by exposure to the gas pressure. The contact unit includes a contact element that is movable relative to the stationary connection contacts by being subjected to the gas pressure generated and that, as a result of the subjection to the gas pressure generated, is moved in the direction of the axis of the contact unit from its starting position to an end position, in which the electrical connection is interrupted via the contact unit.
This switch is designed such that there is no movement to the outside whatever of any parts. Moreover, in an activation, no dangerous gases or fragments whatever escape to the outside.
However, it has been found that this switch unit is only limitedly suitable for switching off relatively high voltages, since then there is the danger that an electric arc is created by the interruption of the separation region as a consequence of the outward motion of the torn-apart ends of the separation region. Experiments on using an extinguishing agent which, in the starting state before activation, surrounds the separation region have shown that the desired success is not achieved thereby; that is, the occurrence of an electric arc is not avoided, or an already-existing electric arc is not reliably extinguished.
Based on this prior art, it is an object of the invention to create a pyrotechnical interruption switch, in particular for interrupting high currents at high voltages, in which the shutoff of high currents at high voltages is also securely ensured by avoiding a current maintained by an electric arc. Moreover, a switch is to be created which in terms of safety is completely unobjectionable and can be produced in a simple and economical way.